Rearrangement hotspots in the sex chromosome of the Palearctic black fly Simulium bergi (Diptera, Simuliidae)

An extreme example of nonrandom rearrangements, especially inversion breaks, is described in the polytene chromosomes of the black fly Simulium bergi Rubtsov, 1956 from Armenia and Turkey. A total of 48 rearrangements was discovered, relative to the standard banding sequence for the subgenus Simulium Latreille, 1802. One rearrangement, an inversion (IIS-C) in the short arm of the second chromosome, was fixed. Six (12.5%) of the rearrangements were autosomal polymorphisms, and the remaining 41 (85.4%) were sex linked. More than 40 X- and Y-linked rearrangements, predominantly inversions, were clustered in the long arm of the second chromosome (IIL), representing about 15% of the total complement. The pattern conforms to a nonrandom model of chromosome breakage, perhaps associated with an underlying molecular mechanism.